1. Field of the Invention
The present invention relates to a high-precision 3D positioning (or position-finding method) for finding the position of elements or individuals. The precision is, for example, of the order of one meter.
The individuals may be located in an open environment or in an urban environment. The system is called a 3D system because of its ability to single out an individual across several floors for example, thus introducing precision along the z-axis if we take a classic x, y, z system of coordinates.
It can be applied, for example, to locating the position of the members of an action team (of firefighters, doctors, special forces, maintenance teams in high-risk zones etc). It also relates to a wider public including, for example, medical personnel in hospitals, elderly persons in retirement homes, victims of avalanches etc.
2. Description of the Prior Art
The currently used position-finding or positioning techniques draw extensively upon various techniques. Four of them are recalled here below.
1. GPS (“Global Positioning System”) Type Satellite-based Positioning Systems
In a GPS type satellite-based positioning system, the geographical position of a GPS receiver is determined by a triangulation of the pseudo-distances between the receiver and a cluster of satellites. This is possible only if the element or individual to be located is visible to the satellites. This is not the case in a certain number of situations (for example in the case of masking by forest cover, tunnels, operations in buildings, underground parking lots, etc.). Furthermore, the precision of a standard GPS, (processing of the frequency L1, code C/A) is in the range of 25 to 30 meters and therefore does not make for precision in the range of one meter. Furthermore, the precision of GPS systems assisted by pedometer or by an inertial guidance unit, for example, remains limited.
2. Cell Radio Telephony Systems such as the GSM (“Global System for Mobile Communication”) Enabling Mobiles to Communicate by Radio with Other Mobiles or with the Public Switched Telephony Network, by Means of Stations Situated at the Center of each Cell of the Cell Network
In a GSM type communications system, the positions of the mobiles are located by a triangulation of the pseudo-distances measured between the mobile to be identified and the base stations. The initiative for measuring the pseudo-distances is taken either by the base stations neighboring the cell in which the mobile is moving or by the mobile. The precision of the position-finding obtained by this method is related to the density of the base stations: it is about 200 meters in urban areas and 400 meters in rural areas.
3. Radiofreguency Transmission Systems Based on Radio Direction-finding
In these systems, the positions of the mobiles are located:                Either by means of an autonomous search and position-finding device: in this case, the method makes use of a distance measurement by means of a transponder type principle (the search module sends out an interrogation signal to the element whose position is to be found or located, and this element instantaneously sends back the response signal) and a measurement of direction on this response signal. In this case, the method is generally of the “homing” type, i.e. the individual responsible for the search gradually approaches the mobile all long the period of movement. This is a highly uncertain technique because all that is needed is an obstacle to greatly weaken the signal and compromise the precision-finding process. Furthermore, the measurement of direction is often obtained by means of a directional antenna, because of the lack of precision and the space taken up by devices based on the differential measurement of phase between several antennas. This search by directional antenna also raises problems because it is imprecise with respect to the size of the antenna to be implemented.        Or by a triangulation of the pseudo-distances measured between the mobile to be identified and reference stations whose position is perfectly known. These stations are also perfectly synchronized, generally by cable, thus limiting the use to equipped zones only. Furthermore, the precision in these systems is always greatly affected, firstly by simultaneous transmissions (entailing collisions) from elements other than the one whose position is to be found or located and, secondly, by the many multiple paths encountered, especially in premises.4. Badge/Beacon Type Devices        
In systems based on a beacon/badge type device, the zone is equipped with beacons (each beacon demarcating a portion of the zone in the same way as the base stations in the cell networks but with a range of some meters to some tens of meters) and the mobiles are fitted out with a transponder badge (which may be passive or active). The beacons are interconnected by a local area network and, when a mobile passes before one of them, a message is sent to the general monitoring center to update the position file. These systems are not compatible with outdoor use and require installation prior to any use in buildings. Furthermore, the precision of these devices is not greater than that of the range of each of these beacons, i.e. it is of the order of some tens of meters.
The object of the invention in particular is a 3D position-finding system with a precision of one meter for example, outdoors or indoors, at any floor whatsoever, without any interruption of operation.
The idea implemented in the method and in the system consists especially in using a mapping of the places associated with measurements of distance and angle, for example in order to reconstruct the direct paths and/or the multiple paths due to the different obstacles.
The beacons are designed to be easily installed, small-sized and low-cost devices, thus offering the possibility of being mounted on escort vehicles or moved according to the progress of positioning needs or the progress of the search or, again, recovered at the end of operation or, possibly, abandoned.